Authors / CoAuthors
Mernagh, T.P. | Lawrie, K.C. | van Achterbergh, E. | Ryan, C.G.
Abstract
Hydrothermal zircons have been previously reported from F- and/or CO2-rich systems (Rubin et al., 1993), quartz-tourmaline mesothermal gold veins (Claoue-Long et al., 1990; Kerrich and King, 1993), and at the Olympic Dam Cu-uranium deposit (Oreskes and Einaudi, 1990). Zircon mobility has also been inferred from the volatile-induced transport of immobile-element-enriched, magmatic-hydrothermal fluids at shallow levels in high-K calc-alkaline volcanic systems in acid-sulphate hydrothermal alteration of rhyolitic volcanics. However, it has previously been difficult to prove that the zircons were truly hydrothermal in origin. This paper outlines the methods we have used to characterise and chemically fingerprint hydrothermal zircons from porphyry Cu-Au, epithermal and lode gold deposits. Hydrothermal zircons were characterised by the following multi-techniques: (1) their distinct morphology and their paragenetic relationships to the ore and mineral assemblages within the veins, (2) the higher concentration of zircon within the quartz veins relative to that of the host rocks, (3) the abundance of solid (e.g. pyrite, rutile, arsenopyrite, alunite) and/or fluid inclusions within the zircons, and (4) their trace element zonation as measured by the CSIRO-GEMOC nuclear microprobe. The following table give some examples of elemental enrichment/zonation in hydrothermal zircons examined in our studies: DEPOSIT TYPE ELEMENTAL ZONATION Enterprise Lode Gold Deposit Cu, As, Ag, Sn, Sb, Ba Bottle Creek Lode Gold Deposit Fe, As, Sr, Sn ,Sb, Ba Gidginbung Epithermal Deposit As, Sb, Th, Yb, U, Y, Hf Nena Epithermal Deposit Fe, Cu, Yb, Th, Sn, Sb, Ba The Dam Porphyry Deposit Fe, Cu, Sn ,Sb, Ba Many mineral deposits cannot be precisely dated due to the lack of suitable zircon-bearing host rocks or due to the resetting of other isotopic systems. Mineral deposits are particularly vulnerable to subsequent modification due to their formation in near surface and/or dynamic tectono-magmatic environments. In these instances, U-Pb dating of hydrothermal zircons directly associated with mineralisation may have a particular advantage over other isotopic systems that rely on less stable minerals.
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39293
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- External PublicationAbstract
- ( Theme )
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- geochemistry
- ( Theme )
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- mineral deposits
- Australian and New Zealand Standard Research Classification (ANZSRC)
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- Earth Sciences
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- Published_Internal
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2002-01-01T00:00:00
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